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Fast pyrolysis

Fast pyrolysis is a process in which organic materials are rapidly heated to 450 - 600 °C in the absence of air. Under these conditions, organic vapors, pyrolysis gases and charcoal are produced. The vapors are condensed to bio-oil. Typically, 60-75 wt.% of the feedstock is converted into oil.

Pyrolysis offers the possibility of de-coupling (time, place and scale), easy handling of the liquids and a more consistent quality compared to any solid biomass. With fast pyrolysis a clean liquid is produced as an intermediate suitable for a wide variety of applications.

The rotating cone reactor

BTG’s fast pyrolysis process is based on the rotating cone reactor developed by the University of Twente. Biomass particles at room temperature and hot sand particles are introduced near the bottom of the cone where the solids are mixed and transported upwards by the rotating action of the cone. In this type of reactor, rapid heating and a short gas phase residence time can be realized.

The initial work of the University of Twente has been the basis for BTG to further develop the pyrolysis reactor and the overall process. Since 1993 BTG has been involved in numerous projects on fast pyrolysis.

BTG’s fast pyrolysis process

A process flow diagram of BTG’s fast pyrolysis process is given below.

Biomass particles are fed near the bottom of the pyrolysis reactor together with an excess flow of hot heat carrier material such as sand, where it is being pyrolysed. The produced vapours pass through several cyclones before entering the condenser, in which the vapours are quenched by re-circulated oil. The pyrolysis reactor is integrated in a circulating sand system composed of a riser, a fluidized bed char combustor, the pyrolysis reactor, and a down-comer. In this concept, char is burned with air to provide the heat required for the pyrolysis process. Oil is the main product; non-condensable pyrolysis gases are combusted and can be used e.g. to generate additional steam. Excess heat can be used for drying the feedstock.

Two test facilities are available in BTG’s lab. A small unit (2- 3 kg/hr) to enable rapid screening of potential feedstocks, and a 100 - 200 kg/hr pilot plant. The latter one provides reliable and representative data for a full scale plant. For further information please see our page on the flash pyrolysis test facility. The pilot plant has processed in total over 70 tonnes of oil for a number of clients.

Pyrolysis oil properties

Due to large amounts of oxygenated components present, the oil has a polar nature and does not mix readily with hydrocarbons. The degradation products from the biomass constituents include organic acids (like formic and acetic acid), giving the oil its low pH. Water is an integral part of the single-phase chemical solution. The (hydrophilic) bio-oils have water contents of typically 15 - 35 wt.%. Typically, phase separation does occur when the water content is higher than about 30 to 45 %. Below an example of properties from typical wood-derived pyrolysis oil is given.

Full scale plant

A 2 tonnes/hr fast pyrolysis plant has been designed, constructed and delivered to Malaysia. In the factory - located closely to an existing palm mill - Empty Fruit Bunches (EFB) are converted into pyrolysis oil. Usually, the wet EFB (moisture ~ 65wt%) are combusted on-site yielding only ash which can be recycled to the plantations. The palm-mill produces about 6 t/hr of this wet EFB. The EFB can be converted into pyrolysis oil using BTG’s fast pyrolysis technology. Prior to feeding it to the pyrolysis plant the EFB is further sized and dried. In a drier the moisture content is reduced down to about 5-10%. In this way, all the wet EFB from the palm is converted into approximately 1.2 t/hr pyrolysis oil.

In Hengelo (the Netherlands) a 5 tonnes/hr pyrolysis plant is planned. This unit will convert wood into pyrolysis oil, process steam and electricity. For further details see the project website of the EMPYRO plant. BTG has established a daughter company BTG Bioliquids BV to further implement and commercialize the fast pyrolysis technology in close cooperation with Tree Power. An artist impression of a pyrolysis turbine is available at the website of the architect.

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